International Journal of Computer Applications (0975 – 8887) Volume 36– No.5, December 2011 25 Design of Load-frequency Controller using Artificial Bee Colony Algorithm for an Interconnected Power System Coordinated with UPFC and RFB B. Paramasivam Assistant Professor Department of Electrical Engineering Annamalai University, Annamalainagar Tamilnadu, India, Pin-608002 I.A. Chidambaram Professor Department of Electrical Engineering Annamalai University, Annamalainagar Tamilnadu, India, Pin-608002 ABSTRACT This paper proposes a sophisticated application of Redox Flow Batteries (RFB) coordinated with Unified Power Flow Controller (UPFC) for the improvement of Load Frequency Control (LFC) of a multi- unit multi- area power system. The UPFC offers an effective means to enhance improvement in the power transfer capability of the tie-line. The main application of UPFC is to stabilize the frequency oscillations of the inter-area mode in the interconnected power system by the dynamic control of tie-line power flow. The Redox flow batteries, which are not aged to the frequent charging and discharging, have a quick response and outstanding function during overload conditions. In addition to leveling load, the battery is advantageous for secondary control in the power system and maintenance of power quality of distributed power resources. The Artificial Bee Colony (ABC) algorithm is used to optimize the parameters of UPFC and the cost function of the two area power system along with the integral controller. Simulation studies reveal that the frequency control concept and control design of a RFB coordinated with UPFC units enhance the inertia centre mode as well as inter-area oscillation modes interms of peak deviations and settling time as compared to the output responses of the system obtained without UPFC and RFB units. Keywords Artificial Bee Colony, Redox Flow Batteries, Unified Power Flow Controller, Load-Frequency Control, Integral Controller, Cost Function. 1. INTRODUCTION Power systems, with the increase in size and complexity, require interconnection between the systems to ensure more reliable power supply even under emergencies by sharing the spinning reserve capacities. In this aspect, the Load-Frequency Control and inter- area tie-line power flow control, a decentralized control scheme or control unit is essential. The paper proposes a control methodology that ensures reliability and quality of power supply, with minimum transient deviations and ensures zero steady state error. The importance of decentralized controllers for multi area load-frequency control system, where in, each area controller uses only the local states for feedback, is well known [1]. The stabilization of frequency oscillations in an interconnected power system becomes challenging when implemented in the future competitive environment. So advanced economic, high efficiency and improved control schemes [2], [3] are required to ensure the power system reliability. The conventional load-frequency controller may no longer be able to attenuate the large frequency oscillation due to the slow response of the governor [4]. The recent advances in power electronics have led to the development of the Flexible Alternating Current Transmission Systems (FACTS). These FACTS devices are capable of controlling the network condition in a very fast manner and because of this reason the usage of FACTS devices are more apt to improve the stability of power system. In recents years, as a innovative research basis new FACTS devices are being introduced to increase power system operations flexibility and controllability, to enhance system stability and to achieve better utilization of existing power system [5]. The Unified Power Flow Controller (UPFC) is member of the FACTS family with very attractive features [6], which are able to control, simultaneously or selectively, all the parameters (voltage, impedance and phase angle) affecting power flow in the transmission line . UPFC which consists of a series and shunt converter connected by a common dc link capacitor can simultaneously perform the function of transmission line real / active power flow control in addition to UPFC bus voltage /shunt reactive power control [7]. The shunt converter of the UPFC controls the UPFC bus voltage/shunt reactive power and dc link capacitor voltage. The series converter of the UPFC controls the transmission line real / active power flows by injecting a series voltage of adjustable magnitude and phase angle [8]. On the other hand the series part known as Static Synchronous Series Compensator (SSSC) can be controlled without restrictions. The phase angle of series voltage can be chosen independently from line current between 0 to 2π, and its magnitude is variable between zero and a defined maximum value. The parallel part known as STATic synchronous COMpensator (STATCOM), injects an almost sinusoidal current of variable magnitude at the point of connection. In [9], a power injection model was used to study the effect of UPFC for improving damping of oscillations with an energy function based control strategy. The power injection model is derived from the power balance equations at the UPFC network interface nodes. Most researches have emphasized the effect of UPFCs on stability improvement and power flow control [10], [11]. In this paper the unified power flow controller
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International Journal of Computer Applications (0975 – 8887)
Volume 36– No.5, December 2011
25
Design of Load-frequency Controller using Artificial
Bee Colony Algorithm for an Interconnected Power
System Coordinated with UPFC and RFB
B. Paramasivam Assistant Professor
Department of Electrical Engineering Annamalai University, Annamalainagar
Tamilnadu, India, Pin-608002
I.A. Chidambaram
Professor Department of Electrical Engineering
Annamalai University, Annamalainagar
Tamilnadu, India, Pin-608002
ABSTRACT
This paper proposes a sophisticated application of Redox Flow
Batteries (RFB) coordinated with Unified Power Flow
Controller (UPFC) for the improvement of Load Frequency
Control (LFC) of a multi- unit multi- area power system. The
UPFC offers an effective means to enhance improvement in the
power transfer capability of the tie-line. The main application of
UPFC is to stabilize the frequency oscillations of the inter-area
mode in the interconnected power system by the dynamic
control of tie-line power flow. The Redox flow batteries, which
are not aged to the frequent charging and discharging, have a
quick response and outstanding function during overload
conditions. In addition to leveling load, the battery is
advantageous for secondary control in the power system and
maintenance of power quality of distributed power resources.
The Artificial Bee Colony (ABC) algorithm is used to optimize
the parameters of UPFC and the cost function of the two area
power system along with the integral controller. Simulation
studies reveal that the frequency control concept and control
design of a RFB coordinated with UPFC units enhance the
inertia centre mode as well as inter-area oscillation modes
interms of peak deviations and settling time as compared to the
output responses of the system obtained without UPFC and RFB
units.
Keywords
Artificial Bee Colony, Redox Flow Batteries, Unified Power
Flow Controller, Load-Frequency Control, Integral Controller,
Cost Function.
1. INTRODUCTION Power systems, with the increase in size and complexity, require
interconnection between the systems to ensure more reliable
power supply even under emergencies by sharing the spinning
reserve capacities. In this aspect, the Load-Frequency Control
and inter- area tie-line power flow control, a decentralized
control scheme or control unit is essential. The paper proposes a
control methodology that ensures reliability and quality of
power supply, with minimum transient deviations and ensures
zero steady state error. The importance of decentralized
controllers for multi area load-frequency control system, where
in, each area controller uses only the local states for feedback, is
well known [1]. The stabilization of frequency oscillations in an
interconnected power system becomes challenging when
implemented in the future competitive environment. So
advanced economic, high efficiency and improved control
schemes [2], [3] are required to ensure the power system
reliability. The conventional load-frequency controller may no
longer be able to attenuate the large frequency oscillation due to
the slow response of the governor [4]. The recent advances in
power electronics have led to the development of the Flexible
Alternating Current Transmission Systems (FACTS). These
FACTS devices are capable of controlling the network condition
in a very fast manner and because of this reason the usage of
FACTS devices are more apt to improve the stability of power
system. In recents years, as a innovative research basis new
FACTS devices are being introduced to increase power system
operations flexibility and controllability, to enhance system
stability and to achieve better utilization of existing power
system [5]. The Unified Power Flow Controller (UPFC) is
member of the FACTS family with very attractive features [6],
which are able to control, simultaneously or selectively, all the
parameters (voltage, impedance and phase angle) affecting
power flow in the transmission line . UPFC which consists of a
series and shunt converter connected by a common dc link
capacitor can simultaneously perform the function of
transmission line real / active power flow control in addition to
UPFC bus voltage /shunt reactive power control [7]. The shunt
converter of the UPFC controls the UPFC bus voltage/shunt
reactive power and dc link capacitor voltage. The series
converter of the UPFC controls the transmission line real / active
power flows by injecting a series voltage of adjustable
magnitude and phase angle [8]. On the other hand the series part
known as Static Synchronous Series Compensator (SSSC) can
be controlled without restrictions. The phase angle of series
voltage can be chosen independently from line current between
0 to 2π, and its magnitude is variable between zero and a defined
maximum value. The parallel part known as STATic
synchronous COMpensator (STATCOM), injects an almost
sinusoidal current of variable magnitude at the point of
connection. In [9], a power injection model was used to study
the effect of UPFC for improving damping of oscillations with
an energy function based control strategy. The power injection
model is derived from the power balance equations at the UPFC
network interface nodes. Most researches have emphasized the
effect of UPFCs on stability improvement and power flow
control [10], [11]. In this paper the unified power flow controller
International Journal of Computer Applications (0975 – 8887)
Volume 36– No.5, December 2011
26
is being installed in series with tie-line between any
interconnected areas, which is used to stabilize the area
frequency oscillations by high speed control of tie-line power
through the interconnections. In addition it can also be expected
that the high speed control of UPFC can be coordinated with
slow speed control of governor system for enhancing
stabilization of area frequency oscillations effectively. Under
these situations, the governor system may no longer be able to
absorb the frequency fluctuations. In order to compensate for
sudden load changes, an active power source with fast response
such as Redox Flow Batteries is expected as the most effective
counter measure. The RFB will, in addition to load leveling, a
function conventionally assigned to them, have a wide range of
applications such as power quality maintenance for
decentralized power supplies. The RFB are the excellent short-
time overload output and the response characteristics possessed
in the particular [15], [16]. The effect of generation control and
the absorption of power fluctuation required for power quality
maintenance are expected. However, it will be difficult to locate
the placement of RFB alone in every possible area in the
interconnected system due to the economical reasons. Therefore
RFB coordinated with UPFC are capable of controlling the
network conditions in a very fast and economical manner.
However, due to the complexity of power system such
as nonlinear load characteristics and variable operating points,
the integral controllers tuning with conventional methods may
be unsuitable for some operating conditions. In literature, few
different control strategies have been suggested based on the
digital, self-tuning, adaptive, variable structure systems and
intelligent/soft computing control. Recently, different
Evolutionary Computation (EC) such as Differential Evolution